1. Field of the Invention
The invention concerns a process of controlling the color-change process of several electrochromic glazings, where the color change of each individual electrochromic glazing is controlled within the color-change interval between an initial value Tstart and a final value Tend by an individual control unit and where the individual control units are activated by a central monitor unit.
Electrochromic glazings are increasingly being used where variable solar control or variable light transmission is desired. Various constructions are used for electrochromic glazings. Usually, electrochromic glazings comprise electrochromic elements with a tungsten-oxide-base electrochromic layer. Such electrochromic elements in particular have proved suitable for large-area glazings where, in addition to the electrode layers necessary for application of electric voltage, as counterpart to the tungsten oxide layer, a transparent oxidic counter-electrode layer acting as ion storage layer and a polymer electrolyte layer arranged between the two are present.
The light transmission of electrochromic glazings is usually varied by the application of a voltage to the electrode layers or by impressing a current. Here, on the one hand the endeavor is to cause the color-change process to take place as rapidly as possible, where it is fundamentally desirable to operate with voltages or currents which are as high as possible. On the other hand, it is necessary to ensure that the electrochromic element of the electrochromic glazing is not permanently damaged by excessive voltages or by the flow of excessively high currents. It is necessary to take into account that the permissible voltages or currents are dependent inter alia on the area and the temperature of the electrochromic glazing. This temperature dependence is especially pronounced in the case of electrochromic elements with polymer electrolyte layers.
2. Discussion of Related Art
From WO 98/37453, a self-calibrating control process for electrochromic elements is known where an electrochromic element is assigned a control unit which regulates the voltage applied to the electrochromic element for a color change as a function of the temperature, of the current flowing and of a series of specified parameters independent of format. The previously known control process serves primarily to set the extreme states xe2x80x9cfully coloredxe2x80x9d or xe2x80x9cfully bleachedxe2x80x9d. It also permits however the setting of intermediate states. The electrochromic element activated in this way can, with the aid of a control unit assigned to it, be set individually to any desired transmission state between the extreme states.
It is known practice to activate several electrochromic glazings with the aid of a central monitor unit and in this way to initiate a color change process simultaneously in several such glazings. It has been found that, on account of differing temperature and differing sizes of the individual glazings, significant differences can occur in the color change velocity of the individual glazings, which leads to the light transmission values of the individual glazings occasionally differing significantly from one another during the color-change process. This leads to an inhomogeneous appearance of the glazings, which is generally undesirable.
The invention is based on the technical problem of improving known control processes such that it permits a largely uniform color change of all simultaneously color-changed electrochromic glazings, without of course excessively prolonging the duration of the color-changing process.
The solution to this problem is the subject of claim 1. Advantageous developments will be found in the Subclaims.
According to the invention, the color-change interval is subdivided into a plurality of subintervals. The color change of the electrochromic glazings takes place step-by-step over these sub-intervals controlled by the individual control units; the central monitor unit does not initiate color change of the electrochromic glazings over a new subinterval until all satisfactorily operating glazings have completed their color change over the preceding subinterval.
Of course, the sizes of the subintervals should be so small that any light transmission differences between individual electrochromic glazings are not visible to the normal observer during color change over a subinterval. It has been found that this can be reliably guaranteed for example with tungsten-oxide-based electrochromic glazings if the size of the subintervals is chosen such that the light transmission factors of the individual glazings during color change over this subinterval differ from one another by a maximum of 5%, preferably at most 3%. The subintervals should not be too small, as on the one hand with decreasing size of the subintervals, measuring errors will increasingly impair the control accuracy of the individual electrochromic glazings, and on the other hand the complexity of control and monitoring as a whole will increase. It has been found that a value of approximately 2% for the variation of the light transmission factor of the electrochromic glazings within a subinterval represents the lower limit which, for the reasons stated, should not normally be undershot.
Observance of the aforementioned maximum deviation of the light transmission factor of individual glazings from that of the other glazings during a subinterval of a color change process can be guaranteed, irrespective of the dimensions and of other variables determining the rate of color change, by the size of the subintervals being chosen such that the light transmission factor of the electrochromic glazings during color change does not vary over each subinterval by more than this maximum permissible light transmission factor difference (which, as already stated, is from experience approximately 5%). It is also possible however, with a known installation situation and with known staggering of size of the glazings whose color is to be changed simultaneously, for the subintervals to be greater, as long as it is ensured that in any case under normal circumstances the light transmission factor of the individual glazings does not deviate at any time by more than 5% from that of the other glazings. In this connection, it has of course to be taken into account that even the glazing changing color slowest, at the time when the glazing changing color fastest has already completed a subinterval, has also covered at least part of the subinterval, so that the actual light transmission factor difference between all glazings involved in combined color change is, at all times during the color change over a subinterval, less than the difference of the light transmission factor of the electrochromic glazings at the beginning and at the end of the subinterval concerned.
The invention is also of course applicable with suitable adaptation to arrangements where the central monitor unit imparts to the control units light transmission values which are not nominal ones, but are different manipulated variables characterizing the state of tinting, for example xe2x80x9c100xe2x80x9d for xe2x80x9cfully coloredxe2x80x9d or xe2x80x9c0xe2x80x9d for xe2x80x9cfully bleachedxe2x80x9d. In these cases as well, the subintervals are to be set according to the invention such that the differences in light transmission factor of the individual glazings remain imperceptible at any time, and in particular do not exceed approximately 5%.
The percentages for the subintervals are of course to be regarded as percentage points, not as relative values. Thus, according to the invention, with a color change from a light transmission factor of 50% to a light transmission factor of 20% and with a specified subinterval value of 5%, a color change will initially take place step-by-step to a light transmission factor of 45%, then to 40%, and so on down to 25% and finally to 20%. In this context the stated values for the light transmission factor are nominal desired values for control of the electrochromic glazings, not necessarily genuine measured light transmission values. Of course, the actual values of the light transmission factor of the electrochromic glazings may deviate slightly therefrom, in particular if the light transmission factor of the individual glazings cannot be measured directly, but is derived indirectly from other measured variables.
It is possible according to the invention to provide for the color-change interval to be subdivided into several subintervals of equal magnitude. Another preferred process provides for at least one subinterval at commencement of a color-change process from bleached to colored to be set smaller than the subsequent intervals. In this way, it is possible to ensure that in the region of high light transmission, in which the human eye is especially sensitive and in which in the case of tungsten-oxide-base operating electrochromic elements a clearly discernible color change takes place, only especially slight deviations in the light transmission factor of the individual glazings are permitted. Then, it is possible to proceed such that, starting from the fully bleached state of the electrochromic glazing, the first two subintervals are assigned a value of 2%, while for the subsequent subintervals a value of 4% is specified.
It is not necessary to provide any special explanation that subdivision of the color-change interval into several subintervals is in fact omitted when only a minor color change of the electrochromic glazings is desired, so that the color-change interval does not exceed the value of the subintervals specified according to the invention.
The control process according to the invention permits simultaneous color change of several electrochromic glass panes with the aid of a central monitor unit irrespective of the type of electrochromic elements used for the eleetrochromic glazings. The central monitor unit only specifies the intermediate color-change states to be set in each case between Tstart and Tend and monitors the color-change process by evaluation of the status indications of the individual control units, without their having to be supplied with information concerning the type, size, temperature or other properties of the individual electrochromic glazings. The central monitor unit can for example be operated manually by a user specifying the final value Tend by means of a keyboard or the like and initiating a color-change process. The invention is however especially suitable for integration of the electrochromic glazings in an energy management system of a building, where a plurality of electrically controllable devices are activated and monitored by a building control center. The modular design of the invention facilitates this integration.
In practice, activation of the individual glazings is preferably to take place such that the values for Tend specified by the central monitor unit and the subintervals to be covered in each case are converted by the individual control units into quantities of charge. In the process, different switch-off criteria can basically be used. A subinterval can for example be evaluated as completed when the quantity of charge previously calculated for this subinterval has flowed. It is also possible to provide for a subinterval being completed when the current flowing through the electrochromic element falls below a specified lower threshold value. Corresponding processes are disclosed for example in WO 98/37453. Other known control processes impress a specified current on the electrochromic element and evaluate the resultant voltage for a switch-off criterion. It is also possible to evaluate several of these switch-off criteria in parallel. It is also possible, according to the coloring state of an electrochromic glazing (fully colored, fully bleached or intermediate state), to apply various switch-off criteria. The control units are either self-calibrating (WO 98/37453) or are supplied with the necessary criteria prior to their use, which permit rapid, reliable color-change of the glazing to be activated by it (for example EP 0 718 667). For reliable color change of electrochromic glazings, suitable control processes are known to the specialist and require no detailed explanation here.
Mostly, the control units will monitor, in addition to the aforementioned switch-off criteria, additional safety criteria with which malfunctions, such as for example short-circuit or wire breaks in the system, overshoot or undershoot of the permissible temperatures of the glazings and of the control units, etc., can be detected. If such a malfunction is detected, the control unit sends a corresponding status indication to the central monitor unit, whereupon the latter assesses the corresponding glazing unit as defective and, according to the nature of the fault, removes it from the scanning routine of the central monitor unit either only for the current subinterval and, if necessary, one or more of the subsequent subintervals or until remedy of the fault and until restart of the system by the user.
In order to prevent the color-change process halting or being retarded on account of an atypical malfunction in a glazing or its control unit, which has been not been recognized as a fault by the control unit or the central monitor unit, provision is made according to a special embodiment of the invention for an individual electrochromic glazing to be classified as not operating satisfactorily from the time at which an upper time limit previously stipulated for the subinterval for this glazing is reached. The central monitor unit removes this electrochromic glazing assessed as being defective from the scanning routine, at least for the current subinterval, and continues the color change over the subsequent subinterval as soon as all other satisfactory glazings have completed color change over the current subinterval. The upper time limits will normally be calculated individually at commencement of a subinterval for each glazing to undergo color change as a function of the coloring state, of the area of the glazing or of the quantity of charge necessary for the subinterval and of the temperature by means of suitable approximation formulae. Alternatively it is also possible to use tables in which are recorded numerical values for the upper time limits applicable in each case to all conceivable states of an electrochromic glazing. The upper time limits should incorporate a sufficient interval from each period of time which can be estimated mathematically for the normally occurring color change for the subinterval for the glazing in question, so that this fault criterion is only applicable in exceptional cases.
The control process according to the invention is comparatively free from faults and to a very large extent prevents the malfunction of individual electrochromic glazings or of the control units assigned to them impairing the color-change process of the other glazings.